A dash is used:
in pairs, to mark off information or ideas that are not essential to an understanding of the rest of the sentence:
Thousands of children – like the girl in this photograph – have been left homeless.
My son – where has he gone? – would like to meet you.
to show other kinds of break in a sentence where a comma, semicolon, or colon would be traditionally used:
One thing’s for sure – he doesn’t want to face the truth.
Things have changed a lot in the last year – mainly for the better.
Dashes are especially common in informal writing, such as personal emails or blogs, but it’s best to use them sparingly when you are writing formally.
Back to punctuation.
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